Drilled Pier Foundation on Expansive Soil
Drilled Pier Foundation on Expansive Soil
(OP)
Hi,
I am designing a foundation on medium expansive soil (PI~30)for a church building. Got couple of questions.
1. Will a church be considered as a commercial building? In taht case, should the design live load be 100psf based on IBC code? I guess that this is a location where lot of people gather in the same time, I considered it as a office building - lobbies and first floor corridor. (
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2. Per geotechnical engineer's report, soil Bearing Capacity is 6000psf with SF=2. Bell Diameter to be 72in or less with 1:3 bell to shaft diameter. if bell diameter exceeds 72in, bell angle to be 60deg with 1:2 bell to shaft diameter. Few columns are to carry around 170kips gravity loads.
Bearing area=(170000lb*2/6000)=57sq.ft
Footing dia = 8.5ft
Shaft dia = 4.25ft
This is too beg for such a small load in structural engineering point of view. Please guide me with an option to handle this case or will I have to stay with the same diameter? I can manage all loads with max 24in dia. shaft per structural calculations. Please advise.
I am designing a foundation on medium expansive soil (PI~30)for a church building. Got couple of questions.
1. Will a church be considered as a commercial building? In taht case, should the design live load be 100psf based on IBC code? I guess that this is a location where lot of people gather in the same time, I considered it as a office building - lobbies and first floor corridor. (
)2. Per geotechnical engineer's report, soil Bearing Capacity is 6000psf with SF=2. Bell Diameter to be 72in or less with 1:3 bell to shaft diameter. if bell diameter exceeds 72in, bell angle to be 60deg with 1:2 bell to shaft diameter. Few columns are to carry around 170kips gravity loads.
Bearing area=(170000lb*2/6000)=57sq.ft
Footing dia = 8.5ft
Shaft dia = 4.25ft
This is too beg for such a small load in structural engineering point of view. Please guide me with an option to handle this case or will I have to stay with the same diameter? I can manage all loads with max 24in dia. shaft per structural calculations. Please advise.






RE: Drilled Pier Foundation on Expansive Soil
If 6,000 psf is an allowable, then you don't need to apply the safety factor again.
Second, if your column load is too big, then reducing pier spacing might be an option. Your column numbers and locations may be fixed in the church design so it may not help much but could reduce pier loads to some extent.
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RE: Drilled Pier Foundation on Expansive Soil
Thank you very much for your quick reply.
Do you think my selection based on IBC is correct (LL=100psf)? or can I go for a lower live load?
Soil report says" Utilizing a min factor of safety of 2 for total load, allowable bearing capacity of the foundation soil at the recommended depth is 6000psf for total load.
I also thought of adding an extra line of columns, but it is not possible.
RE: Drilled Pier Foundation on Expansive Soil
If you needed two piers to keep the sizing down, you could just design an appropriate pile cap.
RE: Drilled Pier Foundation on Expansive Soil
RE: Drilled Pier Foundation on Expansive Soil
Also - based on your posted statement from the soil report - this is an allowable soil load of 6,000 psf. You don't add another safety factor to it.
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RE: Drilled Pier Foundation on Expansive Soil
RE: Drilled Pier Foundation on Expansive Soil
RE: Drilled Pier Foundation on Expansive Soil
RE: Drilled Pier Foundation on Expansive Soil
RE: Drilled Pier Foundation on Expansive Soil
RE: Drilled Pier Foundation on Expansive Soil
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RE: Drilled Pier Foundation on Expansive Soil